1. Field of the Invention
This invention relates to systems for providing a fluid of a select temperature by mixing of two fluids of differing temperatures or by disposition of such fluids in mutual heat tranfer relationship and more particularly to such a system for use in supplying bleed air of a particular temperature from a gas turbine engine.
2. Description of the Prior Art
It is well known to air-condition aircraft cabins and power various aircraft subsystems with air bled from the aircraft's propulsion system. In air-conditioning the cabin of a gas turbine engine powered aircraft, it has been the practice to supply the cabin with air bled from the compressor section of the engine, such air being cooled to the desired temperature by mixture or mutual heat tranfer with cooler air supplied by the engine's fan. Inasmuch as differing engine operating conditions cause variations in the temperature of the compressor bleed air, systems which monitor the temperature of the bleed air and cool the bleed air with a controlled flow of cooler fan air are necessitated. Such systems have in the past been of two general types. The first type as exemplified by the systems disclosed in U.S. Pat. Nos. 3,441,213 and 3,537,644 each assigned to the assignee of the present invention, generally comprises a pneumatic temperature sensor controlling a pneumatic fan air modulating or control valve. While such pneumatic temperature sensors exhibit fairly accurate steady state response, it has been found that the transient performance of such sensors could be improved upon. While certain fast-acting pneumatic or mechanical temperature sensing transducers have been proposed, the accuracy of such sensing devices has been found inadequate for aircraft cabin air-conditioning systems.
Other proposed fluid temperature control systems such as that shown in U.S. Pat. No. 2,919,859 to Krueger employ electrical temperature sensors, and controls, and, while such systems may exhibit both adequate steady state accuracy and rapid transient response, they require the disposition of rather delicate electrical sensors and connectors in the hostile environment of the gas turbine engine and therefore are subject to damage from heat and/or vibration resulting in poor system reliability.
It is therefore an object of the present invention to provide a fluid temperature control system which overcomes the deficiencies of the prior art.
It is another object of the present invention to provide such a fluid temperature control system of enhanced steady state accuracy.
It is another object of the present invention to provide a fluid temperature control system which responds rapidly to sudden changes in inlet fluid temperature.
It is another object of the present invention to provide a fluid temperature control system which employs no electrical components.
It is another object of the present invention to provide such a fluid temperature control system of enhanced reliability.